Field of the Invention
The present invention relates to a dynamic analysis system.
Description of Related Art
Traditional acquisition of static radiographic (X-ray) images has used a film/screen or photostimulable phosphor plate to assist medical diagnosis. Recent studies have focused on acquiring a dynamic image of a portion to be inspected (hereinafter referred to as “target portion”) using a semiconductor image sensor (e.g., a flat panel detector (FPD)) and applying the image to medical diagnosis. This technique is based on the quick responsibility of the semiconductor image sensor in reading and deleting image data. In detail, the technique involves continuous emission of pulsed radiation from a radiation source in accordance with the timings of reading and deletion of the semiconductor image sensor, and acquisition of multiple images per second to capture dynamic states of the target portion. The series of acquired images are sequentially displayed to allow a doctor to observe a series of movements of the target portion.
In inspection of lungs, detection of a portion having a defective function (ventilatory or blood flow function) has high importance. Unfortunately, doctors cannot readily find a portion having a defective function based on visual observation of a dynamic image. In particular, the individual variations in respiratory movements of lungs and heartbeats make it harder to visually recognize a portion having a defective ventilatory or blood flow function.
To solve this problem, some systems analyze dynamic images acquired by dynamic imaging and generate diagnosis-assisting information to be provided to doctors for early diagnosis.
For example, PTL 1 (Japanese Patent No. 4404291) discloses a system that generates differential images between frames of a dynamic image during respiration. The system then determines a differential pixel having the maximum absolute value in each group of corresponding pixels of the differential images between frames, and generates a maximum-value image consisting of these differential pixels. The system displays the generated image superimposed on an image in a predetermined respiratory phase.
PTL 2 (Japanese Patent No. 5093727) discloses a system that calculates pixel values within a predetermined range in each of the frame images constituting an X-ray dynamic image, and generates blood-flow information indicating a temporal variation in the pixel values varying in response to heartbeats. The system also detects a boundary portion between a lung field region and a heart in each frame image, and calculates the movement of the boundary portion as the movement of a core wall.
Measurement of lung compliance is considered effective to diagnose respiratory problems. The lung compliance is an index indicating the flexibility of a lung. A lung having high lung compliance readily expands. This lung has low elastic recoil and causes excess expansion, and thus precludes rapid expiration. In other words, this lung does not readily contract. The lung having high lung compliance may have problems, such as pulmonary emphysema, COPD, and a pulmonary cystic disease. In contrast, a lung having low lung compliance is inflexible and cannot sufficiently expand regardless of movement of inspiratory muscles. In other words, this lung does not readily expand, and readily contracts. The lung having low lung compliance may have problems, such as a restrictive lung disease, interstitial pneumonia, pulmonary fibrosis, and pulmonary edema.
The lung compliance is measured by inserting a tube through the nose to the esophagus and detecting the pressure in the esophagus. Unfortunately, this method places a large burden on a test subject, requires large tasks, and cannot provide any stable value, and thus is not practically applied. Another problem of the method is that it cannot provide local lung compliances, despite differences in lung compliance from place to place in a diseased lung.
Measurement of the flexibility (hardness) of pulmonary vessels is considered effective to diagnose arteriosclerosis and pulmonary hypertension. The hardness of blood vessels is generally measured. For example, four sphygmomanometers are mounted on the right and left arms and ankles to contemporarily measure blood pressures. In diagnosis of arteriosclerosis, the vascular diameter in the neck is determined by echography.
Unfortunately, these methods for measuring the hardness of blood vessels cannot be applied to the evaluation of the flexibility of pulmonary vessels.
The system disclosed in PTL 1 or 2 analyzes a dynamic image to calculate information effective in inspection of the ventilatory and blood flow functions of a lung, but cannot determine the flexibility of a lung field or pulmonary vessels.